It is known to sever continuous lengths of materials into discrete increments by passing the material between a backup roll and a series of radially projecting cutting or chopper blades mounted and spaced evenly about the periphery of a blade roll.
A typical prior art blade roll may comprise a stainless steel blade roll cylinder member which has been milled in order to provide a plurality of cutting or chopper blade supporting slots. In U.S. Pat. No. 3,869,268 chopper blade supporting slots are milled with a thickness which is larger than the thickness of generally rectangular chopper blades which are mounted in the cylinder member. This is done in order to avoid the excessive cost of milling each slot to the exact thickness of an individual chopper blade. However, by milling the slots to be somewhat larger than the chopper blades, e.g., 0.002-0.004 inch, the blades tend to vibrate within the slots during operation of the blade roll. Movement of a cutting blade radially outward and circumferentially of the supporting blade roll is disclosed as being reduced in U.S. Pat. No. 3,869,268 by the use of semi-circular protrusions which are formed on end fasteners holding the cutting blades. However, vibration facilitated by the oversized slots tends to cause the chopper blades to wear more rapidly thus shortening the effective life of the chopper blades. The semi-circular protrusions also tend to set up deleterious stress concentrations within the mating parts. In order to more firmly hold chopper blades in position in a blade roll, U.S. Pat. Nos. 3,508,461 and 3,644,109 incorporate a resilient gasket mounted in contact with the side edges of chopper blades having generally trapezoidal cross-sections. In use, after the chopper blades are positioned in the blade roll an end cap is fastened securely to the blade roll which abuttingly engages the resilient gasket. The end caps are tightly fastened against a respective gasket in order to rigidly fix the blades so that outward and circumferential movement of the blades from the blade roll member may be prevented. In tightly fastening the end caps against the gasket the blades are often forced to cut through the resilient gasket such that the ability of the gasket to retain the chopper blades in position is not only destroyed but other hazards may be created. These hazards include the random and unpredictable motion of gasket fragments which may fly out and contaminate the material being chopped, or in an extreme case strike an operator of the chopper assembly. In all likelihood, the blades must be cut to an exact length in order to reduce this problem.
U.S. Pat. No. 4,083,279 provides a chopper blade retaining means for a blade roll which comprises an annular blade retainer positioned at each end of a blade roll cylinder member. A side surface of each of the blade retainers has at least one annular groove which may be situated radially inwardly of the outer diameter of the blade roll cylinder member when the centerline of each blade retainer is in alignment with the centerline of the blade roll cylinder member. A blade retaining ring made of copper is positioned partially within the at least one annular groove of each blade retainer such that the blade retaining rings engage each side edge of the chopper blades in order to restrain each chopper blade against movement in a circumferential and radial direction. While very useful, the blade retaining means of U.S. Pat. No. 4,083,279 suffers from several disadvantages. For example the chopper blades cannot be used directly as received from the manufacturer because the chopper blades vary in length by as much as 0.20-0.28" and the structural relationships of the various components cannot account for such a variance in blade lengths. It is therefore usually necessary to grind the chopper blades to an exact length. Since machining costs are high it is usually uneconomical and therefore undesirable to grind the chopper blades to an exact length which is suitable for the particular apparatus. Further, the chopper blade retaining rings cannot be reused because as each annular blade retainer is tightened against the blade roll cylinder member the copper retaining rings are crushed by the blades and will "cold flow" around and grip the ends of the chopper blades. After such force has been applied and the chopper blades have been used, the blade retaining rings will have a series of permanent indentations. The copper blade retaining rings thus have to be changed every time the blade roll is serviced. Finally, end stresses on the chopper blades induced by the constraint of the blade retaining rings on the ends of the blades may cause blade breakage thus shortening their effective chopping life.
Accordingly it is an object of the present invention to overcome the disadvantages of prior art blade rolls by providing a blade roll having an improved blade retaining means which increases the effective chopping life of the chopper blades.
It is a further object of the present invention to provide an improved blade retaining means for use in a chopper assembly which substantially eliminates undesirable vibration of the chopper blades mounted within a blade roll cylinder member.
Another object of the present invention is to provide a blade retainer which reduces the contamination of the material being chopped.
A still further object of the present invention is the provision of a constraint on the movement of chopper blades in a chopper assembly in a circumferential and radial direction which allows installation of blades directly as received from the manufacturer.
Still another object of the present invention is the provision of a chopper blade constraint which is safe, has a long service life and can be used repetitively.
An additional object of the present invention is to provide a cushioned support for cutting blades in a blade roll cylinder member thereby reducing blade breakage.
Accordingly, the present invention provides an improved blade retaining means comprising an annular blade retainer positioned at each end of a blade roll cylinder member wherein a side surface of each of the blade retainers has at least one annular groove situated radially inwardly of the outer diameter of the blade roll cylinder member when the centerline of the blade retainer is in alignment with the centerline of the blade roll cylinder member. A blade retaining urethane ring is positioned at least partially within the annular groove of each blade retainer so that the blade retaining ring engages the chopper blades at each end thereof thereby restraining the chopper blades against movement in a circumferential and radial direction.